Per(halo-oxygen) acid oxidation,purification and recovery process

ABSTRACT

AN ELECTRODIALYTIC APPARATUS UTILIZING ANION AND CATION PERMSELECTIVE MEMBRANES AND HAVING AT LEAST ONE TWOCHAMBER CELL FOR PURIFICATION AND AT LEAST ONE THREECHAMBER CELL PROXIMAL THE TWO-CHAMBER UNIT FOR CONCENTRATION OF AQUEOUS PER(HALO-OXYGEN) ACIDS AND THEIR SALTS, ALL ANOLTE CHAMBERS SHARING A COMMON ANOLYTE STREAM, ALL CATHOLYTE CHAMBERS SHARING A COMMON CATHOLYTE STREAM, AND AT LEAST ONE OF THE ANOLYTE CHAMBERS OF THE PURIFICATION AND THE CONCENTRATION CELLS SHARING A COMMON ANODE. A MULTI-STEP PROCESS FOR RECOVERING AND REGENERATING THE PERIODATE OXIDANT USED IN PREPARING OXIDIZED POLYSACCHARIDES IN WHICH THE PRIMARY LIQUOR AND SUBSEQUENT WASH LIQUORS FROM THE OXIDIZED POLYSACCHARIDE FILTER CAKE ARE CIRCULATED IN THE ANOLYTE AND MIDDLE CHAMBERS OF THE ELECTRODIALYTIC APPARATUS HAVING TWO-CHAMBER AND THREECHAMBER CELLS FOR RE-OXIDATION AND CENCENTRATION RESPECTIVELY, THE LIQUORS HAVING A CONCENTRATION OF 1 TO 15 WEIGHT PERCENT BEING CIRCULATED IN THE ANOLYTE CHAMBERS; THOSE LIQUORS HAVING A CONCENTRATION OF 0.5 TO 5 WEIGHT PERCENT BEING CIRCULATED IN THE MIDDLE CHAMBER, ALL LIQUORS AND EFFLUENTS HAVING A CONCENTRATION OF LESS THAN 0.5 WEIGHT PERCENT BEING PASSED THROUGH A STRONG BASE ANION EXCHANGE RESIN WHICH REMOVES THE REMAINING PERIODATE OR CHEMICALLY REDUCED PERIODATES, WHICH ARE SUBSEQUENTLY ELUTED BY THE SODIUM HYDROXIDE CATHOLYTE, WHICH IN TURN IS CIRCULATED IN THE ANOLYTE CHAMBERS OF THE APPARATUS FOR REGENERATION.

Ag. 1, 1972 A. H HEl-r ErAL PER(HALOOXYGEN) ACID OXIDATION, PURFICATIONAND RECOVERY PROCESS 2 Sheets-Sheet 1 original Filed April 3,' 1968PER(HALO 1 1 m/Q QJ.. lllllJ. m mtsoru mws@ 2.55m M z Eloi H5012@ T T TJ. ,ml Szm n @z mmlv 1 l woxfmox 55%# v 7 l NO Szm@ oxmox I #OX T.' .l xm f No N @magma Il ONZ- .Fm l l m l OMEQIMZU Omr m2mmv +r f f loxmlx IvNox |10 v l v l N m H E mmzmw o U /Nlomz l o \|1Swmzmw ommw L f Swzmw ,vH -o++I4oN1 -o++14o-1 -Io+N1+o-I ,\w l N N Smwz ,r Smzm@ @M5525 #6+...lo I H woxmoxwx +I 1v 1| +1 U W um, in@ N @nl o @d mm :L 7 R F q L. an 9 u Y q Nl i m L m United States Patent Oce 3,681,213 Patented Aug. l,1972 3,681,213 PER(HALO0XYGEN) ACID OXIDATION, PURIFI- CATION ANDRECOVERY PROCESS Allyn Harold Heit, Mount Holly, and James NorrisWilliamson, Marlton, NJ., assgnors to Sybron Corporation, Rochester,N.Y.

Original application Apr. 8, 1968, Ser. No. 719,361., now Patent No.3,607,694, dated Sept. 21, 1971. Divided and this application Oct. 7,1970, Ser. No. 78,986

Int. Cl. C01b 11/26 U.S. Cl. 204-82 6 Claims ABSTRACT OF THE DISCLOSUREAn electrodialytic apparatus utilizing anion and cation permselectivemembranes and having at least one twochamber cell for purification andat least one threechamber cell proximal the two-chamber unit forconcentration of aqueous per(halo-oxygen) acids and their salts, allanolyte chambers* sharing a common anolyte stream, all catholytechambers Asharing a common catholyte stream, and 'at least one' of the.anolyte chambers of the purication and the concentration cells sharinga common anode. lAv multi-step process for recovering and regeneratingthe periodate oxidant used in preparing oxidized polysaccharides inwhich the primary liquor and subsequent wash liquors from the oxidizedpolysaccharide iilter cake are circulated in the anolyte and middlechambers of the electrodialytic apparatus having two-chamber andthreechamber cells for re-oxidation and concentration respectively, theliquors having a concentration of 1 to 15 Weight percent beingcirculated in the anolyte chambers; those liquors having a concentrationof 0.5 to Weight percent being circulated in the middle chamber, allliquors and `eliiuents having a concentration of less than 0.5 weightpercent being passed through a strong base anion exchange resinWhichremoves the remaining periodate or chemically reduced periodates,which are subsequently Veluted by the sodium hydroxide catholyte, whichin turn is circulated in the anolyte chambers of the apparatus forregeneration.

CROSS-REFERENCES TO RELATED APPLICATIONS This is a division ofapplication Ser. No. 719,361, tiled Apr. 8, 19168, now U.S. Pat. No.3,607,694.

This invention relates generally to a process for the electrolyticrecovery and regeneration of inorganic halogen acids and their salts andan apparatus therefor. More particularly it relates to a method for theelectrodialytic recovery, and regeneration of periodic acid and itsSalts,

' and re-use of the periodic acid and its salts in the oxidation ofpolysaccharides.

The Malaprade reaction is an illustration of the application of periodicacid and its salts in organic oxidations. This reaction consists in thetreatment of an orlganic material having vicinal hydroxy groups witheither periodic acid or an al-kali metal periodate resulting (a) in theconversion of the vicinal hydroxy groups to aldehyde and (b) in theconversion of the periodic acid or the periodate salt to a chemicallyreduced form such as, iodic acid or its salts. The reaction may be shownas:

IIB-d- H10, arb-H H10, H20 0H 0H (1)l (2) (3) where (l) represents thevicinal hydroxy groups such as those found in starch or cellulose, (2)represents the aldehyde group and (3) represents the chemicallyrereaction may be illustrated by the conversion of starch regardless ofvegetable origin, to so-called dialdehyde starch as represented by (2)in the above reaction. The.

starches and celluloses so treated are members of the class designatedas polysaccharides, and the products, polysaccharides oxidized byperiodic acid and its salts, may be referred to as oxidizedpolysaccharides.

The production of dialdehyde starch and other oxidized polysaccharideshas attained commercial status, and due to the expense involved in theuse of the expensive periodic acid and its salts as oxidants, and theneed for a more efficient and economical process for the production ofthe oxidized polysaccharides has arisen. Public concern and legislationalso require' the development of methods resulting in the absence ofcontamination and pollution of rivers, lakes, underground Water tablesand the like, from the discharge of process efiluents. Several methods,both electrolytic and chemical and combinations thereof, have beendeveloped for the production of dialdehyde starch and other oxidizedpolysaccharides; however, none-of these electrolytic methods areeconomically capable of any more than oxidation of chemically reducedperiodic acid or its salts present in liquors in excess of 4 Weightpercent of the periodic acid or its salts. It is therefore the primaryobject of this invention to provide an electrolytic apparatus in whichchemically reduced oxidants in the form of inorganic ion dissociablematerials may be electrolytically oxidized simultaneously with theelectrolytic concentration of the oxidants and chemically reducedoxidants.

It has been shown in U.S. 2,648,629 and U.S. 2,713,- 553 thatpolysaccharide materials can be oxidized in a two-chamber electrolyticcell in which periodic acid is formed and simultaneously consumed by thestarch. It has also been demonstrated in U.S. 2,830,941 that alkalimetal periodate can be prepared electrolytically by a separate unitoperation thereby eliminating the various complications attending themaintenance of a starchlodate slurry within the electrolytic cell. U.S.2,648,629,

- U.S. 2,713,553 and U.S. l3,131,137 set forth design rparameters oftwo-chamber periodate cells. 'I'he electrolytic cells which are used inconnection with the oxidation of polysaccharides and .are disclosed inthe prior art 1n general share the following features: (i1) open-cellstructure, (2) use of alundum thimbles as barriers between catholyte andanolyte chambers, (3) planar rectangular or cylindrical lead anodes, (4)rod or tube steel cathodes and (5) circulation of anolyte by agitatoraction or pumping from a reservoir.

An electrolytic cell having multiples of a two-chamber unit beendisclosed in Industrial and Engineering Chemlstry, Process Design andDevelopment, vol. 1, page 144 1962). Each two-chamber unit has ananolyte chamber and a catholyte chamber separated by a diaphragm. Usingiodio acid as anolyte and sodium hydroxide as catholyte, periodic acidcan be formed at the anode -When a potential difference is appliedacross the electrodes. In a typical example using this prior artmultiple unit electrolytic cell a starch slurry (not within the cell) isfirst oxidized to dialdehyde starch by means of a periodic acidsolution. A filter cake of the oxidized starch is separated from theslurry, and the acidic iodate-rich liquor obtained after separation iscycled through an evaporator where much of the water is removed. Theacidic iodate-rich liquor concentrated by evaporation is circulated inthe anolyte chamber of the electrolytic cell where the periodic acid isregenerated at the anode. A 5% sodium hydroxide catholyte solution isused in the catholyte chamber of the cell. Small quantities of thecatholyte solution are added to the anolyte solution to maintain the pHas required.

These prior art electrolytic cells and processes suffer from severalmajor deficiencies, which in the main, have prevented their commercialacceptance. Among them is the fact that no provision is made forhandling the dilute wash waters and other efiiuents which contain about01.011 to 4.0 weight percent of periodic acid, and its salts andchemically-reduced periodic acid and its salts except for a separateconcentrating lby flash evaporation. As a practical matter recovery isgenerally postulated on only 8 to 10 weight percent iodate liquors inthe prior art processes.

Evaporation is unavoidably limited to the stronger concentrations of thedilute wash Waters by reason of the economics of evaporation techniques.The presence of heat in such evaporation techniques leads to thedecomposition of the acidic solutions of iodine-containing acids andtheir salts through interaction with various organic materials, such as,oils, fats, protein residues and water soluble extracts, leached intothe slurries and liquors from the polysaccharides under treatment orformed from the polysaccharides 'by a hydrolytic or oxidativedegradation of the starch. Therefore, it is an object-of this inventionto provide a process for the oxidation of polysaccharides in which allperiodic acid and its salts and chemically reduced periodic acid and itssalts present in wash waters and liquors are recovered and regeneratedwithout resorting to destructive evaporation techniques.

The prior art electrolytic cells and processes suffer from otherdisadvantages which include a limitation upon current densities due toinadequate electrolyte circulation rates of aqueous solutions ofperiodic acid and its salts; no provision for the circulation ofcatholyte except by periodic semi-manual emptying of reservoirs when theconcentration of caustic becomes excessive; and partial utilization ofthe lead anode surfaces. Therefore, it is an object of this invention toprovide an electrolytic apparatus for the purification and concentrationof inorganic ion dissociable materials in which anolyte and catholyteare continuously circulated in a closed system and the surfaces of thelead anodes are completely utilized.

Another object of this invention is to provide a process cation cell ormultiples thereof and the other section having a three-chamber unitdesignated as a concentration cell or multiples thereof. Thepurification and concentration sections are physically integrated into aunit construction in such a manner that the purification section ormultiples thereof are proximal the concentration section or multiplesthereof within a single frame. Both the purifcation and concentrationsections derive current from a common direct current power source,derive catholyte from a common closed catholyte circulating system andderive anolyte from a common closed anolyte circulating system. Thepurification section of the electrolytic apparatus consists of at leastone two-chamber arrangement characterized by an anolyte chamber, ananode having a surface in the anolyte chamber in contact with theanolyte, a catholyte chamber, a cathode having a surface in the anolytechamber in contact with the catholyte, and a cation permselectivemembrane separating the chambers, one surface of which serves as abarrier for the anolyte chamber and the other surface of which serves asa barrier for the catholyte chamber, all elements being mounted within asuitable frame.

The concentration section mounted proximal to the purification sectionwithin the same suitable frame, consists of at least one three-chamberarrangement characterized by an anolyte chamber, an anode having asurface in the anolyte chamber in contact with the anolyte, a middlechamber, au anion permselective membrane separating the anolyte chamberfrom the middle chamber, a catholyte chamber, a cathode having a surfacein the catholyte chamber in contact with the catholyte and apermselective membrane separating the catholyte chamber from the middlechamber. All membranes serve as barriers for the chambers which theyseparate. The permselective membrane utilized to separate the catholytechamber from the middle chamber may be either an anion permselectivemembrane or a cation permselective membrane. All anolyte chambers in thepurification section of the apparatus are connected by pipe or suitableconduit to all anolyte chambers in the concentration section and shareacommon anolyte reservoir. All catholyte chambers in the purificationsection of the apparatus are connected .by pipe or suitable conduit toall catholyte chambers in the concentration section and share a commoncatholyte reservoir.

The preferred kmultiple-cell purification section is constructed in sucha manner that there is maximum utilization of the anode surface. Thus,one anode may serve as the anode fortwo anolyte chambers. In thepreferred multiple-cell purification section one catholyte chamber andits circulating stream of catholyte liquor serves two anolyte chambersand streams, one of the anolyte chambers being located on one side ofthe catholyte chamber.

and the other located on the opposite side of the catholyte chamber withnecessary permselective membranes and other required elements insertedtherebetween.

The preferred multiple-cell concentration section is constructed in sucha manner that there is maximum utilization of the anode surface. Thus,one anode serves as the anode for two anolyte chambers. In the preferredmultiple-cell embodiment one catholyte chamber and its circulatingstream in the concentration section serves two middle chambers andstreams. In the preferred embodiment of the apparatus having aconcentration section and a purification system, at least one of theanolyte chambers` "l of a concentration section and the purificationsection share a common anode. However, cell construction may be variedto permit a chamber arrangement in which at least one catholyte chamberof the purification section and at least one catholyte chamber of theconcentration section share a common anode. Although the preferred cellarrangement is designated above, we do not intendto limit the unitconstruction and the general plan of anolyte and catholyte systemscommon to both purification and concentration systems to any specificarrangement of electrolyte chambers, electrodes and the like.

The function of the purification section of the electrolytic apparatusis the regeneration of chemically reduced inorganic per(halo-oxygen)acids and their salts at the anode and the removal of cations from theanolyte liquor. Such chemically reduced inorganic per(halooxygen) acidsand their salts which may be regenerated in the anolyte chambers includechemically reduced periodic acid, sodium periodate, perchloric acid,sodium perchlorate, ammonium perchlorate or mixtures of such iodates,chlorates, periodates and perchlorates combined with such cations asNa+, H+, NH4+. The oxygen required for the necessary regeneration isgenerated by the electrolytic decomposition of water at the anode. Thus,iodide anion will be oxidized to iodate anion which will be furtheroxidized to periodate anion at the anode. This oxidation process at theanode is accompanied by a simultaneous migration of cations across thecation permselective membrane separating the anolyte and catholytechambers Vfrom the anolyte liquor to the caustic catholyte liquor. Inthis way undesirable cations, such as, sodium,

ammonium and the like may be removed from the anolyte liquor, hence thedesignation of this section or cell as the purication section. Thepreferred caustic catholyte liquorY tration section of the electrolyticapparatus is the concentration of inorganic per(halooxygen) anions andtheir chemically reduced derivatives including iodate, chlorate, iodideand chloride. These per(halooxygen) anions may be paired with a cationor a combination of such cations as sodium cation, ammonium anion andhydrogen. The v periodate, iodate and like anions initially in themiddlechamber and designated as dialysate, migrate from the middlechamber toward the anode through the anion permselective membrane `intothe anolyte. Concurrently with the concentrating function the anolytechamber also functions in the oxidative regeneration of the chemicallyreduced per(halooxygen)l anions and their salts in the same way that theanolyte chamber of the purication section regenerates the chemicallyreduced acids and their salts. Since an anion permselective membrane isused between the anolyte and middle chambers, anions are permitted topass from the middle chamber to the anolyte chamber while cations areprohibited from migrating from the anolyte chamber to the middlechamber. The iodate-periodate or other per(halooxygen) anions or theirchemically reduced derivatives which migrate from the middle stream arereplaced predominantly by hydroxyl anions migrating toward the anodefrom the catholyte chamberwhen the kpermselective membrane between thecatholyte and middle chambers is an anion permselective membrane. Bythis mechanism the anolyte liquor becomes enriched with the iodate,periodate or any other halogen anion derivative which may be present,While the middle chamber electrolyte (dialysate), subsequently destinedfor waste or further treatment by an anion exchange resin bed, isdepleted in iodate, periodate and other halogen anion derivatives.

A cation permselective membrane may also be used between the catholyteand middle chambers. lWhen this arrangement is used the cations presentin the dialysate circulating in the middle chamber migrate toward thecathode through the cation permselective membrane into the catholyteliquor where they unite with the hydroxyl ion retained in the catholyteliquor by reason of the cation permselective barrier. The dialysatecirculated in the middle chamber may be an aqueous solution of per(halooxygen) acids and their salts and chemically reduced derivativesthereof.y

Suitable anion and cation exchange membranes which must remain stablefor long periods of exposure to the corrosive action of the liquid mediaused as circulating liquors, were used in the electrodialytic apparatus.The" Ionac Chemical Company 3400 series permselective membranes haveproven suciently durable to withstand such corrosivity and may be usedin the apparatus of this invention.

The electrodialytic cell of this invention -is constructed in such a Waythat the entiresystem including all chambers, electrodes and circulatingsystems can operate simultaneously at full eiciency. Any individualsection or unit of the electrodialytic apparatus may be disengaged fromoperation while other sections or units of the cell continue to operateefficiently. This can be accomplished by merely obstructing thecirculating stream to any individual chamber or section.

The anodes used in the electrodialytic cell of this invention arepreferably of a silver-lead alloy containing approximately 1% silver.Both sides of each lead anode 6 plate are used to supply current to ananolyte chamber in the preferred embodiment of this invention. Thus, atypical purification section in a multiple-cell arrangement may have thefollowing series of elements; an anolyte chamber at the end of the unit,then a catholyte chamber, an anolyte chamber, an anolyte chamber, acatholyte chamber and the like. A typical concentration section in amultiple-cell arrangement may have the following series of elements; acatholyte chamber, middle chamber, anolyte chamber, anolyte chamber'middle chamber, catholyte chamber and the like. Terminal anolytechambers are served by a single anode and terminal catholyte chambersserve a single anolyte chamber in the preferred embodiment. l

During the operation of the electrolytic apparatus the effectivediiference in potential -is considered to be that amount of currentwhich will cause (a) the migration of a sucient number of anions andcations to substantially vary the concentrations of the liquors withinthe chambers in a designated interval of time and (b) the oxidation orregeneration of a substantial number of the chemically reduced inorganicanions within a designated interval of time.

In relation to the electrolytic apparatus of this invention we have alsofound a process for quantitatively recovering and regenerating theperiodate oxidant used in preparing oxidized polysaccharides. The rststep in this process is the separation, water washing and drying ofoxidized polysaccharides in successive steps to form a solid product andas many aqueous liquors as necessary to substantially remove allperiodate and chemically reduced periodate anions from the solid ltercake by successive water washings.

In the preferred embodiment of the process for oxidiz ingpolysaccharides the primary liquor obtained from the ltration of themother liquor from the oxidized polysaccharide has a periodate andchemically reduced periodate anion concentration of about 4 to 15 Weightpercent. Washing of the lilter cake with either de-ionized water orwater from which all periodate and chemically reduced periodate anionshave been removed and hereafter designated as de-anionized water,produces a secondary liquor having from :about 1 to 8 weight percent ofperiodate and chemically reduced periodate anions. Subsequent washingsof the filter cake as `above produce a tertiary liquor having lliquorsmay be subsequently concentrated to about 5 to 15 weight percent ofperiodate and chemically reduced periodate anions, and the chemicallyreduced periodate anions may be oxidized to periodate anions for re-usein oxidizing polysaccharides.

All of the aqueous periodate and chemically reduced periodate anionspresent in the liquors obtained fromrthe filtering and Washing of thefilter cake in which the concentration of the periodate and chemicallyreduced periodate anion concentration is in excess of about 0.5 weightpercent, may be concentrated to about 5 to 15 Weight percent bycirculating the liquor in the middle chamber of the concentration cellset out above. All aqueous periodate and chemically reduced periodateanions present in the liquors obtained from the washing and filtering ofthe filter cake in which the concentration of the periodate andchemically reduced periodate anion concentration is less than about 0.5weight percent, may be concentrated by ion accumulation on an anionexchange resin. The anions accumulated ou the anion exchange resin maybe eluted from` the resin by using an aqueous caustic solution and inthe preferred embodiment may be eluted by the caustic catholyte liquorfrom the electrolytic apparatus discussed above. The eluate may then becirculated in the anolyte chamber of the electrolytic apparatus wherethe chemically reduced periodate anions, such as, sodium iodate,

Will be oxidized to the periodate anion. All references to periodateanions refer to periodic acid as -Well as to its sodium and other salts.

All chemically reduced periodate anions are circulated in the anolytechamber of the electrodialytic apparatus to convert the chemicallyreduced periodate anion to the periodate anion.

When the aqueous liquors having from about 0.5 to weight percent ofperiodate and chemically reduced periodate anions are circulated in themiddle chamber of the electrolytic apparatus, the periodate andchemically reduced periodate anions migrate across the anionpermselective membrane to the anolyte chamber to provide an aqueoussolution in the anolyte chamber of about 5 to weight percent periodatevand chemically reduced periodate anions. The chemically reducedperiodate anions which have migrated to the anolyte chamber of theconcentration section, are then oxid-ized to periodate anions in theanolyte chambers of both the concentration and purification sections.The middle chamber efliuent which may be designated as a quinary liquor,contains about 0.01 to 0.5 weight percent periodate and chemicallyreduced periodate and is passed through the anion exchange resin toremove substantially all traces of the periodate and chemically reducedperiodate anions. The same ion exchange resin bed may be used to removeperiodate and chemically reduced periodate from the quaternary andquinary liquors. The efiiuent from the anion exchange resin bed iscompletely de-anionized. By de-anionized we mean that all periodate andchemically reduced periodate anions are removed from the efliuent.

A suitable ion exchange resin for the removal ofthe periodate andchemically reduced periodate anions is a strong base polystyrene alkylquaternary ammonium ion exchange resin in the sulfate form manufacturedby Ionac Chemical Company as Ionac A-540. This ion exchange resininsures complete removal of all traces of iodine, iodic acid, periodicacid and their salts from the efiiuent water which may be utilized insubsequent washing of oxidized polysaccharide filter cakes or may bediscarded as waste.

A complete understanding of the invention may be obtained from thefollowing description and explanation which refer to the accompanyingdrawings illustrating an embodiment directed to the recovery andregeneration of periodic acid and its salts and chemically reducedderivatives thereof.

FIG. 1 is a diagrammatic representation of a process for oxidizingpolysaccharides and recovering and regenerating the periodate oxidantused in oxidizing the polysaccharide.

FIG. 2 is a diagrammatic representation of a longitudinal cross-sectionof an electrolytic cell.

Referring to FIG. 1, a polysaccharide and anolyte from the streamdesignated as 19d containing regenerated periodic acid and its salts ina concentration of about 5-15 weight percent taken from anolytereservoir R-11, are reacted in an ordinary reactor. The resultingoxidized polysaccharide slurry is filtered at filter step 1 resulting inthe separation of the primary liquor from the primary wet solids. Theprimary liquor, which contains less than `5-15 weight percent ofunreacted periodic acid and its salts and chemically reduced periodicacid and its salts, is returned to reservoir R-11 by conduit 19a forsubsequent re-oxidation in the anolyte chambers 11a and 11b of theelectrolytic apparatus.

The primary wet solids are then washed or slurried with de-anionizedwater-1, which may be completely de-ionized water or water in whichperiodate and chemically reduced periodate anions have been removed, toform mixture 1. Mixture 1 is filtered at filter step 2 resulting in theseparation of secondary wet solids and secondary liquor. The secondaryliquor containing about 1 to 8 weight percent periodate and chemicallyreduced periodate is added to anolyte reservoir R-11 by means of conduit19b. Thus,

8 the primaryand secondary liquors are returned to anolyte reservoir.R-11 for subsequent re-oxidationy in anolyte chambers 11a and 11b of theelectrolytic apparatus.

The secondary wet solids are washed or slurried with de-anionizedwater-2 to form mixture 2. Mixture 2 is filtered by standard filtrationtechniques in filter step 3 to provide a tertiary liquor and tertiarywet solids. lThe tertiary liquor having a periodate and chemicallyreduced periodate concentration of about 0.5 to 5 weight percent passesto middle chamber reservoir R-12 bymeans of conduit 20a to become theliquor designated as dialysate or electrodialysate. The dialysate iscirculated bymeans of conduit 20 to, through and from the middle chamber12 of the electrolytic apparatus. When the concentration of thedialysate in Vreservoir R-12 reaches about 0.01 to 0.5 weight percent ofperiodate and chemically reduced periodate anions, the dialysate ispassed to an anion exchange resin bed or column by means of conduit 2Gb.As the dialysate liquor passes through the anion exchange resin theperiodate and chemically reduced periodate anions accumulate on theanion exchange resin, and the effluent stream, 20d, passing from the,anion exchange resin bed, is designated de-anionized water-4.De-anionzed water-4 has no trace of periodate or chemically reducedperiodate anions until the anion exchange resin has been exhausted andrequires regeneration. However, de-anionized water4 may contain hydroxylanion. De-anionized water-4 may be used as wash waters designed asdeanionized water-1, -2 and 3, or it may be discarded as waste fromwhich all periodate and chemically reduced periodate anions have beenremoved. De-anionized water- 1, -2 and -3 may be any type of waterpurified by distillation or ion exchange processes.

The tertiary wet solids are washed or slurried with de-anionized water-3to form mixture3. Mixture 3 is filtered at filter step 4 producing areduced periodate impoverished liquor and a wet solid product. 'I'.hewet solid product is an oxidized polysaccharide which is subsequentlydried to form a dry solid product useful as fabric softeners and thelike. The `reduced periodateimpover.-` ished liquor, the quaternaryliquor, has a periodate and chemically reduced .periodatel anionconcentration of about 0.01 to 0.5 Weight percent and is passed byconduit 21 to the anion exchange resin bed where the periodate anionsare accumulated on the anion exchange resin, and the etliuent designatedas 2lb is added tothe deanionized water-4 in a manner similar to thatexplained for the dialysate eluent which passes through conduitzob. Y

The periodate and chemically reduced periodate anions which haveaccumulated on the anion exchange resin may be eluted from the resin bycaustic catholyte from Catholyte reservoir R-13. The caustic Catholyte,which has a concentration of about 5 to 10 weight percent sodiumhydroxide, passes by conduit 18a to the anion exchange resin. Theperiodate and chemically reduced periodate anions are eluted from theanion exchange resin and pass by conduit 19c to anolyte reservoir R-11for re-oxidation of the chemically reduced periodate, and the anionexchange resin is regenerated for subsequent removal of periodateanions. An evaporator may be placed in conduit 19C to concentrate theeluate prior to addition to reservoir R-11.

Catholyte reservoir supplies Catholyte to Catholyte chambers 13a and 13bby means of conduit 18. The electrolytic apparatus designated in FIG. 1is a five chamber unit in which chambers 11a, 12 and 13a derivingelectrical potential from anode 10a and cathode 14, form theconcentration section of the cell. The purification section of the cellwhich derives electrical potential from anode 10b and cathode 14, vismade up of chambers 13b and 11b. Anolyte chamber 11b and Catholytechamber 13b are separated by cation permselective membrane 17. Anolytechamber 11a and middle chamber 12 are separated by anion permselective'membrane 15b. The anion permselective membrane 15b may be replaced by acation permselective membrane with no ladverse effect upon the over-allrecovery and regeneration scheme. Anolyte chambers 11a and 11b aresupplied by a common anolyte conduit 19 from anolyte reservoir R-11,both c harnbers being interconnected via conduit 19 and reservoir R-11.Catholyte chambers 13a and 13b are supplied by a common catholyteconduit 18 `from catholyte reservoir R-13 both chambers beinginterconnectedV via conduit 18 and catholyte reservoir R-13.

FIG. 2 represents a cross section of a tive-chambered unit in whichoxidation,purification and concentration of typical periodate andchemically reduced periodate anions are depicted as simultaneouslyoccurring in a twochamber purification section located proximal to athreechamber concentration section. In the over-all'cell construction,the five chambers designated as 13a, 11a, 11b, 12 and 13b are heldwithin a single frame designated as 16. The frame 16 may be any materialcapable of withstanding the corrosive action of the liquors and havingsuitable structural strength and rigidity to withstand mild temperatureincreases and the weight of the liquors and other structural components.Anolyte chambers 11a and 11b are interconnected by means of a commonconduit designated as 19. Catholyte chambers 13a and 13b areinterconnected by means of a common conduit designated as 18. Thepurification section of the cell which comprises catholyte chamber 13aand anolyte chamber 11a are supplied with direct current by cathode 14aand anode respectively. Chambers 13a and 11a are separated by cationpermselective membrane 17. The concentration section of the cell whichcomprises catholyte chamber 13b, anolyte chamber 11b andmiddle chamber12 are supplied with direct current by anode 10, a surface of whichdefines anolyte chamber 11b, and cathode 14b, a surface of which definescatholyte chamber 13b. The middle chamber 12 is defined by anionpermselective membrane.

a which separates the middle chamber from the anolyte chamber, and anionpermselective membrane 15b which separates the middle chamber from thecatholyte chamber.

In FIG. 2, when ay caustic catholyte is circulated in catholyte chambers13a and 13b, an aqueous anolyte containing X", XO3- and X04- iscirculated in anolyte chambers 11a and 11b, and an electrodialysatecontaining X", XO3- and X04- is circulated in middle chamber 1,2, whereX,-, XO3- and X04- represent periodate and chemically reducedperiodateanions or perchlorate and chemically reduced perchlorate anions andwhere all electrolytes contain cations which may be Na+ and H+, ormixtures thereof, designated as kf', the following reactions andmigrations occur simultaneously when an electrical potential is appliedto the anode and cathodes:

(1) X-, XOaand X04- anions migrate from the electrodialysate in chamber12 to the anolyte in chamber 11b;

(2) k+ cation is retained by action of the anion permselective membranein chamber 12 where it unites with OH- anion migrating from thecatholyte in chamber 13b where it is generated;

(3) H2O and alkali metal hydroxides present in catholyte chambers 13aand 13b generate molecular hydrogen and OH- anion; the OH- anionmigrates from the catholyte in chamber 13b to chamber 12 through anionpermselective membrane 15b and which is retained in chamber 13a byaction of cation permselective membrane 17, while the k+ formed inchambers 13a and 13b is retained by the action of the cathodes;

(4) H+ and molecular oxygen are generated in anolyte chambers 11a and11b by electrolytic action on water at the anode; the generated oxygenin combination with the electrical charge resulting in the oxidation ofall chemically reduced XO.,- anions to X04- anions which are shown ingeneration at anode 10` in chambers 11a and 11b by the electrolyticoxidation steps of X-aXOaand XO3- XO4-; and

` (5) k+ cations are retained in chamber 11b by the action of anionpermselective membrane 15a and migrate from the anolyte in chamber 11athrough cation permselective membrane 17 to the catholyte in 13a in thedirection of cathode 14a where k+ is retained by the action of thecathode 14a.

Therefore, the chemically reduced X04- anions are regenerated inchambers 11a and 11b; the X-, X03- and X04- present in the dialysate inchamber 12 areconcentrated by transfer to chamber 11b; and undesirablecations, k+ are removed from the anolyte in chamber 11a by transfer ormigration to the catholyte in chamber 13a.

The following specific examples are provided to further illustrate thepractice of this invention.

Example I A multi-chambered electrodialytic cell was constructed byplacing a series of purification sections consisting of the followingarrangement of chambers; anolyte, catholyte, anolyte, anolyte,catholyte, anolyte, anolyte, catholyte, etc. with a total of sevencatholyte chambers, and thirteen anolyte chambers in conjunction with aseries of concentration sections consisting of the following arrangementof chambers; catholyte, middle, anolyte, anolyte, middle, catholyte,middle, anolyte, etc. With a total of four anolyte chambers, threecatholyte charnbers and four middle chambers. The concentration andpurification section chambers, cathodes and anodes were assembled withina common framework. lAssembly of the apparatus was such that a maximumnumber of anolyte compartments utilized a minimum number of silver-leadanodes. All anolyte chambers of both sections Were supplied with anolytefrom a common anolyte circulating system and trough. All catholytechambers of both sections were supplied with caustic catholyte from acommon catholyte circulating system and reservoir. The middle chambersof the concentration section were provided with a circulating systemwhich circulated the middle chamber compartment electrolyte. An ionexchange column containing a highly basic anion exchange resin wasprovided for removal of iodine derivative residues from spent middlechamber electrolyte. Regeneration of the spent anion exchange resin wasaccomplished by passing the caustic catholyte through the anion exchangeresin bed. Provision was made for the transfer of the elutediodine-containing catholyte to the anolyte stream to minimize the lossof iodine or its derivatives.

Each chamber was one inch thick with minor variations due to gaskets andelectrodes and defined a working area of four square feet. Membraneswere heterogeneous in nature and constructed on a webbing of inactivesupporting fibers by means of an inert binder. In the primary section ofthe electrodialytic apparatus the anolyte and catholyte compartmentswere separated by cation permselective membranes. Anion permselectivemembranes were used between the anolyte and middle chambers andcatholyte and middle chambers of the concentration sectiou. IonacChemical Company 3400 series of membranes which have proven stable forlong periods of exposure to the corrosive action of the liquid mediaused in the circulating streams, were used in the electrodialyticapparatus. Anodes were formed from a lead alloy comprising about 1%silver, and the perforated cathode was formed from a mild steel.

The catholyte was a 5% sodium hydroxide solution. The anolyte was theprimary filtrate from a periodic acid oxidation of starch for theproduction of dialdehyde starch and consisted of unreacted periodate andiodate anions. The iodate was present from the reduction of periodateduring the polysaccharide oxidation. The solution in the middlecompartments of the concentration section consisted of the diluteiodate-periodate-containing washings from the dialdehyde starch filtercake.

Anolyte, 85 gallons, with a total iodate-periodate concentration(calculated as periodate) of 83.2 grams/liter was circulated through theanolyte system common to both the purification and concentrationsections. The actual periodate concentration of the anolyte was 64.0grams/ liter. Therefore, 77.0% of the anolyte was periodic acid. TheNaOH catholyte was circulated through the catholyte system common toboth sections. A volume of 70 gallons of dilute wash water wascirculated through the middle chamber of the concentration section. Thetotal iodine content of the dilute wash water was 9.9 grams/ liter(calculated as periodate).

Voltage was applied at the electrodes by means of a rectifier, and thecurrent of the system was maintained at approximately 1200 amps. Thetemperature was normally 35-40" C.

The table following shows the results of the electrodialyticregeneration and concentration. The column represented as Total underMiddle represents the total concentration of iodate and periodate(calculated as periodate) in grams/liter in the middle compartment ofthe concentration section.

l Calculated as periodate.

The table shows that the concentration of periodate and percentperiodate increases with time, indicative of regeneration of periodatefrom iodate in the liquor. The total concentration of theiodate-periodate liquor in the middle compartment decreases with timeindicative of removal of the iodine derivatives from the middle stream.

The dilute Wash waters were cycled through the middle chamber of theconcentration section until the iodate concentration of the middlestream was 1.5 g./l. The 70 gallons of liquor in the middle stream wasthen cycled through an ion exchange column consisting of 1.5 cu. ft. ofstrong base polystyrene alkyl quaternary ammonium ion exchange resin inthe sulfate form, manufactured by Ionac Chemical Company as Ionac A540.The eluted liquor contained no trace of iodine or its derivatives andwas discharged into the sewer.

The strong base ion exchange resin was exhausted after eluting severalother cycles of iodate-containing liquor through the column. Exhaustionof the resin can be determined by the presence of iodate in the elutedliquor. The ion exchange resin was then regenerated by passing thecaustic catholyte from the catholyte circulating system through theresin bed. The eluted liquor was added to the anolyte system forregeneration.

Example II In an electrodialytic regeneration and concentration of thefiltrates from a periodic acid conversionV of cellulose to dialdehydecellulose the same apparatus, method and quantities were used as givenin Example I. The following table showing v the total concentration ofiodateperiodate in grams/ liter in the anolyte and middle streams andthe concentration and percent periodate in the anolyte 12 in relation tolength of time of operation of the apparatus at a current of 1200 ampsinput is lgiven below.

Middle Anolyte chamber Total 1 Periodate (conc.) (conc.) Percent TotaLlg./l. g./l periodate g. /1.

1 Calculated as periodate.

It can be seen from examination of the data thatthe percentage ofperiodate in the anolyte increases with time. Note that within 11.5hours the periodate concentration of the anolyte more than doubled. Thetotal concentration of the iodate-periodate in the middle chamber wasreduced indicating that the apparatus has concentrated the anolyte andremoved iodate-periodate from the dilute wash waters. The dilute washwaters upon reaching a concentration of 1.5 g./1. in the middlecirculating stream were cycled through the strong base ion exchangeresin resulting in complete removal of iodine and its derivatives.'y

Example III The anolyte, catholyte and middle chambers of theconcentration section of the apparatus were disconnected from theircirculating systems by merely clamping ol the hoses leading to thesechambers, and the purification section of the cell was operated alone.The operating conditions and capacities with the exception of theremoval of the concentration section from operation, were the same asthose given in Example I. The table below shows the results of theregeneration of periodate from the spent liquors filtered fromdialdehyde starch product.

Anolyte Total 1 conc.,

g./1. (Iodate- Periodate Percent Time, hrs. periodoate) conc., g./1.periodate 1 Calculated as periodate.

The data show that the percent and concentration of iodate in theanolyte increase with time during the operation of the apparatus,indicating that the purification section may be operated independentlyof the concentration section.

Example 11V The anolyte and catholyte chambers of the purificationsection of the apparatus were disconnected from their circulatingsystems by merely clamping off the hose leading to those chambers, andthe concentration section of the cellv was operated alone. The operatingcapacities and conditions with the exception of the removal of thepurification section from operation, were the same as those given inExample I. 'Ihe table following shows the results of the concentrationof the anolyte byremoval of the iodate and periodate remaining in thedialdehyde starch wash waters.

Anolyte Y Middle Total 1V periodate Total Time, hrs. cogli?? com/:1.,cognjl:

l Calculated as periodate.

The data indicate that the total iodate-periodate concentration of themiddle chamber in the concentration section decreases with acorresponding increase in the total iodate-periodate concentration andin the periodate the concentration in relation to the length of timethat the apparatus is in operation, indicating that the concentrationsection of the apparatus may be operated independently of the primarysection.

The apparatus constructed according to this invention is suitable forthe oxidation of chemically reduced per- (halo-oxygen) acids and theirsalts to per(halooxygen) acids and their salts which may be used tooxidize polysaccharides. Special application of the apparatus to theoxidation, purification and recovery of periodate and chemically reducedperiodate anions which were recovered from liquors of oxidizedpolysaccharides, was successful.

The present invention provides a process for the purification andconcentration of periodate and chemically reduced periodate anions withsubstantially complete recovery of all periodate and chemically reducedperiodate anions by a combination of an electrolytic technique and anion exchange technique. The present invention also provides a singleelectrolytic apparatus in which concentration, purification andoxidation may be carried out simultaneously.

It is to be understood that the invention is not to be limited by theseexamples or by the specific reaction conditions, construction materials,concentrations of liquors and the like, but includes variations andmodifications falling within the scope of the appended claims anddrawings.

We claim:

1. A process for quantitatively recovering and regenerating theperiodate oxidant used in preparing oxidized polysaccharides,comprising:

(a) separating, water washing and drying the oxidized polysaccharides insuccessive steps to form a solid product and a plurality of aqueousliquors containing at least one of the members selected from the groupconsisting of periodate, iodate iodide and other halogen anionderivatives whereby substantially all periodate, iodate and iodide arerecovered in the aqueous liquors in successively diminishingconcentrations;

(b) circulating the aqueous liquors having a concentration in excess ofabout 0.5 weight percent in the middle chamber of an electrodialyticapparatus having, in combination a two chamber unit purification cellcomprising an anolyte chamber containing circulating aqueous anolyte, ananode having a surface in the anolyte chamber in contact with theanolyte, a catholyte chamber containing circulating aqueous catholyte, acathode having a surface in the catholyte chamber in contact with thecatholyte, and a cation permselective membrane separating the chambers,one surface being in contact with the anolyte and the other surface withthe catholyte; a three-chamber unit concentration cell proximal thepurification cell comprising an anolyte chamber containing circulatingaqueous anolyte, an anode having a surface in the anolyte chamber incontact with the anolyte, a middle chamber, an anion permselectivemembrane separating the anolyte and middleA chambers, one surface beingin Contact with the anolyte and the other surface being in contact withthe aqueous liquors, a catholyte chamber containing circulating aqueouscatholyte, a cathode having a surface in the catholyte chamber incontact with the catholyte and a permselective membrane separating thecatholyte and middle chamber, one surface being in contact with thecatholyte and the other surface in contact with the aqueous liquor, both2-chamber and 3chamber units being within a frame; means for circulatinga common stream of aqueousanolyte to, through and from the anolytechambers of the purification and concentration cells; means forcirculating the aqueous liquor to, through and from the middle chamberof the concentration cell; means` for circulating a common stream ofaqueous catholyte to, through and from the catholyte chambers of thepurification and concentration cells; and means for imposing a commondifference in potential across the anodes and cathodes of thepurification and concentration cells;

(c) concentrating the periodate, iodate and iodide anions in the aqueousliquors by establishing a potential across the apparatus wherebyperiodate, iodate and iodide anions migrate from the middle chamber tothe anolyte chamber of the concentration cell where said anions areoxidized and circulate with the common stream of aqueous anolyte;

(d) concentrating all periodate, iodate and iodide present in liquors inconcentrations less than about 0.5 Weight percent by ion accumulation onan anion exchange resin;

(e) eluting the periodate, iodate and iodide anions from the anionexchange resin;

(f) circulating the eluate from the anion exchange resin in the anolytechamber; and

(g) oxidizing the iodate and iodide anions by circulating the liquors inthe anolyte chamber and establishing a potential across the apparatus,whereby an aqueous periodate solution lsuitable for re-use as an oxidantis obtained.

2. A process as defined in claim 1 wherein the separating and waterwashing are sequentially repeated upon the oxidized polysaccharide toprovide four aqueous solutions comprising a primary liquor having fromabout 4 to l5 weight percent of periodate, iodate and iodide anions, asecondary liquor having from about 1 to 8 weight percent of periodate,iodate and iodide anions, and each liquor having from about 0.5 to 5weight percent of periodate, iodate and iodide anions, and a quaternaryliquor having from about '0.01 to I0.5 Weight percent of periodate,iodate and iodide anions, whereby each liquor is suitable for subsequentconcentration to about 5 to 15 weight percent of periodate, iodate andiodide aninons, and each liquor is suitable for subsequent oxidation ofiodate and iodide anions to periodate for re-use in oxidizingpolysaccharides.

3. A process as defined by claim 1 wherein the aqueous liquors havingfrom about 0.5 to 5 weight percent of periodate, iodate and iodide arecirculated in the middle chamber whereby the periodate, iodate andiodide anions migrate across the anion permselective membrane to theanolyte chamber when a potential is established across the apparatus, toprovide an aqueous solution in the' anolyte chamber of about 5 to 15weight percent periodate, iodate and iodide anions, the iodate andiodide anions which have migrated to the anolyte chamber, being oxidizedto periodate anions, and the middle chamber efiluent containing fromabout 0.01 to 0.5 weight percent periodate, iodate and iodide anions.

4. A process as defined by claim 3 wherein the effluent from the middlechambers, the effluent containing from about 0.01 to 0.5 weight percentperiodate, iodate and iodide anions, is concentrated by passing theefiluent through the anion exchange resin bed.

5. A process as defined by claim 1 wherein the aqueous liquors havingfrom about 1 to 15 weight percent of periodate, iodate and iodide arecirculated in the anolyte chamber whereby iodate and iodide anions areoxidized to 15 16 periodate anions by electrolytic action at the anodelwhen v v y, References Cited a potential is established acrosstheapparatus. 4 UNITED STATES PATENTS 6. A lprocess as defined =by claim 1wherein the per- Y f v Y odate, iodate and iodide anions are eluted fromthe anion 2,8310941 4/1958, Mehltretter 204-782 exchange resin bypassing the aqueous basic catholyte 5 3131137 4-/1964 Lancaster et al'204.42

from `the catholyte chamber through the anion exchange FREDERICK CEDMUNDSON primar Exam-mer resin bed, whereby the anion exchange resinbed is ret, y y t generated for further use and the periodate, riodateand U.S. C1. X.R. iodide are made available for subsequent processing.204-95 ggo -UN1TED STATESv PATENT OFFICE CERTIFICATE OF- CORRECTON Y.

Patet N5.' 3,681,213 l Dated August-14, 1972y nvetods) Allyn H. Heit andJames Norris Williamson It ie certified that error appears :1.11A theabove-identified patent and that-said Letters Patent are herebycorrected'as shown'below:

E ln the specification, column 6 line l0 insert a comma after chamber(second occurrence). Column l0, line 2, XO3" should read X03 Column12,'line 70, delete 25.4" and substitute therefor 26.4 v

In the claims, claim 2, column 14, actual line 4l, delete and eachl andsubstitute therefor a tertiary..

Claim .4, column 14, actual line 47, correct theuspelling of "anions..

'Signed and sealed this 2nd day of January .1973.

(SEAL) Attest:

EDWARDM.FLETCHER,JR. l ROBERT GOTTSCHALK Attesting: lOfficerCommissioner of EPatent

